1. Field of the Invention
The present invention relates to a semiconductor type physical quantity sensor which can be used as, for example, a pressure sensor for detecting an intake pressure of an engine in an automobile.
2. Description of Related Art
FIG. 9 shows the constitution of a conventional semiconductor type pressure sensor. A diaphragm 1a is formed in a silicon substrate (sensor chip) 1. The diaphragm 1a is displaced in accordance with pressure applied thereto. A plurality of diffusion gauges (strain gauges) 2 are formed on a surface of the diaphragm 1a. Resistance values of the diffusion gauges 2 vary in correspondence to displacement of the diaphragm 1a. The silicon substrate 1 is bonded to a glass pedestal 3 by anodic-bonding. A vacuum chamber 4 is formed between the silicon substrate 1 and the glass pedestal 3. As a result, the diaphragm 1a is displaced in accordance with a differential pressure between pressure applied to an upper surface of the diaphragm 1a and pressure in the vacuum chamber 4. A unit including the silicon substrate 1 bonded to the glass pedestal 3 constitutes a sensing unit 5. The glass pedestal 3 is soldered on a base 6, such as a metal stem, with the result that the sensing unit 5 is mounted on the base 6.
In the constitution as described above, when the base 6 is formed from a resin material for example, the base 6 is likely to be deformed. If the base 6 is cramped at right and left side-faces (A and A' faces) in the figure and is not cramped at front and rear faces (B and B' faces) in the figure, the base 6 is deformed as shown in FIG. 10 on the basis of its thermal expansion. That is, the base 6 is greatly distorted in an X direction rather than in a Y direction as shown in FIG. 10. The distortion of the base 6 is transmitted to the silicon substrate 1 via the glass pedestal 3. As a result, large stress is generated in the X direction on the surface of the silicon substrate 1. When the diffusion gauges 2 formed on the surface of the silicon substrate 1 detect such stress biased in one direction, a detection error in the detecting operation of the diffusion gauges 2 occurs.